Methods, apparatus, and systems for power efficient d2d communications for wearable and iot devices

ABSTRACT

Method, apparatus, and system for establishing and conducting device to device communications in a radio network.

FIELD

The present invention relates to the field of wireless communicationsand, more particularly, to methods, apparatus and systems for effectingdevice-to-device (D2D) communications in wireless communicationnetworks.

BACKGROUND

Direct device-to-device (D2D) communications has received a lot ofinterest recently as major standardization bodies such as IEEE and 3GPPhave defined, or are in the process of defining, specifications tosupport D2D communications. In the case of 3GPP and LTE-based radioaccess, support for D2D communications is being introduced to allow forcost-efficient and high-capability public safety communications usingLTE technology. This is primarily motivated by the desire to harmonizethe radio access technology across jurisdictions in order to lower thecapital expense and operating expense of radio-access technologyavailable for the use of public safety (PS) types of applications.Another significant motivating factor is the fact that LTE is a scalablewideband radio solution that allows for efficient multiplexing ofdifferent service types like voice and video.

Since Public Safety (PS) applications often require radio communicationsin areas that are not under radio coverage of an LTE network, e.g. intunnels, in deep basements, or following catastrophic system outages,there is a desire to support D2D communications for PS in the absence ofany operating network or prior to the arrival of AdHoc deployed radioinfrastructure. However, even when operating in the presence ofoperating network infrastructure, PS communications typically still willrequire higher reliability than commercial services.

PS type applications, e.g. between first responders, will very likelyinclude direct push-to-talk speech services using multiple talk groups.Additionally, to make efficient use of the capabilities an LTE broadbandradio provides, PS type applications may include services such as videopush or download.

It is expected that once deployed, D2D communications will be available,not only for PS type applications, but also for commercial uses. Oneexample may be the case of utility companies, which often also requiresupport for 2-way radio communications in areas not covered by networkinfrastructure. Furthermore, D2D services such as Discovery are suitablesignaling mechanisms to allow for proximity-based services and trafficoffload using LTE-based radio access in commercial use cases.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the Detailed Descriptionbelow, given by way of example in conjunction with drawings appendedhereto. Figures in such drawings, like the detailed description, areexamples. As such, the Figures and the detailed description are not tobe considered limiting, and other equally effective examples arepossible and likely.

Furthermore, like reference numerals in the figures indicate likeelements, and wherein:

FIG. 1A is a system diagram illustrating an example communicationssystem in which one or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram illustrating an example wirelesstransmit/receive unit (WTRU) that may be used within the communicationssystem illustrated in FIG. 1A according to an embodiment;

FIG. 1C is a system diagram illustrating an example radio access networkand another example core network that may be used within thecommunications system illustrated in FIG. 1A according to an embodiment;

FIG. 1D is a system diagram illustrating another example radio accessnetwork and another example core network that may be used within thecommunications system illustrated in FIG. 1A according to an embodiment;

FIG. 1E is a system diagram illustrating a further example radio accessnetwork and a further example core network that may be used within thecommunications system illustrated in FIG. 1A according to an embodiment;

FIG. 2 is a block diagram illustrating the basic communicationarchitecture for D2D communications in a radio access network;

FIG. 3A is a diagram illustrating signal flow for establishing andperforming D2D communications in a radio network in accordance with oneMME based relay UE selection exemplary embodiment;

FIG. 3B is a diagram illustrating signal flow for establishing andperforming D2D communications in a radio network in accordance with oneremote UE based relay UE selection exemplary embodiment and

FIG. 4 shows NAS message structure in accordance with one exemplaryembodiment.

DETAILED DESCRIPTION

A detailed description of illustrative embodiments may now be describedwith reference to the figures. However, while the present invention maybe described in connection with representative embodiments, it is notlimited thereto and it is to be understood that other embodiments may beused or modifications and additions may be made to the describedembodiments for performing the same function of the present inventionwithout deviating therefrom.

Although the representative embodiments are generally shown hereafterusing wireless network architectures, any number of different networkarchitectures may be used including networks with wired componentsand/or wireless components, for example.

I. Example Networks for Implementation

The present disclosure focuses on improvements for D2D communications inthe next generation of 3GPP LTE Radio Access Network (RAN) (commonlyreferred to as 5G or New Radio (NR)). However, the concepts andinventions disclosed herein have wider applicability. The following is adescription of the basic structures of some of the more common RANtechnologies and related devices in use today and to which theseconcepts may be applied, including a description of the current 3GPP LTEarchitecture.

FIG. 1A is a diagram illustrating an example communications system 100in which one or more disclosed embodiments may be implemented. Thecommunications system 100 may be a multiple access system that providescontent, such as voice, data, video, messaging, broadcast, etc., tomultiple wireless users. The communications system 100 may enablemultiple wireless users to access such content through the sharing ofsystem resources, including wireless bandwidth. For example, thecommunications systems 100 may employ one or more channel accessmethods, such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 103/104/105, a core network 106/107/109, a publicswitched telephone network (PSTN) 108, the Internet 110, and othernetworks 112, though it will be appreciated that the disclosedembodiments contemplate any number of WTRUs, base stations, networks,and/or network elements. Each of the WTRUs 102 a, 102 b, 102 c, 102 dmay be any type of device configured to operate and/or communicate in awireless environment. By way of example, the WTRUs 102 a, 102 b, 102 c,102 d, any of which may be referred to as a “station” and/or a “STA”,may be configured to transmit and/or receive wireless signals and mayinclude a user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a smartphone, a laptop, a netbook, a personal computer,a wireless sensor, consumer electronics, and the like. Any of the WTRUs102 a, 102 b, 102 c and 102 d may be interchangeably referred to as aUE.

The communications systems 100 may also include a base station 114 aand/or a base station 114 b. Each of the base stations 114 a, 114 b maybe any type of device configured to wirelessly interface with at leastone of the WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to oneor more communication networks, such as the core network 106/107/109,the Internet 110, and/or the other networks 112. By way of example, thebase stations 114 a, 114 b may be a base transceiver station (BTS), aNode-B, an eNode B, a Home Node B, a Home eNode B, a site controller, anaccess point (AP), a wireless router, and the like. While the basestations 114 a, 114 b are each depicted as a single element, it will beappreciated that the base stations 114 a, 114 b may include any numberof interconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 103/104/105, which mayalso include other base stations and/or network elements (not shown),such as a base station controller (BSC), a radio network controller(RNC), relay nodes, etc. The base station 114 a and/or the base station114 b may be configured to transmit and/or receive wireless signalswithin a particular geographic region, which may be referred to as acell (not shown). The cell may further be divided into cell sectors. Forexample, the cell associated with the base station 114 a may be dividedinto three sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and may utilize multiple transceiversfor each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 115/116/117,which may be any suitable wireless communication link (e.g., radiofrequency (RF), microwave, infrared (IR), ultraviolet (UV), visiblelight, etc.). The air interface 115/116/117 may be established using anysuitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 103/104/105 and the WTRUs 102a, 102 b, 102 c may implement a radio technology such as UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA),which may establish the air interface 115/116/117 using wideband CDMA(WCDMA). WCDMA may include communication protocols such as High-SpeedPacket Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may includeHigh-Speed Downlink (DL) Packet Access (HSDPA) and/or High-Speed ULPacket Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface115/116/117 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.11 (i.e.,Wireless Fidelity (WiFi), IEEE 802.16 (i.e., Worldwide Interoperabilityfor Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×, CDMA2000 EV-DO,Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), InterimStandard 856 (IS-856), Global System for Mobile communications (GSM),Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and thelike.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRadio Access Technology (RAT) for facilitating wireless connectivity ina localized area, such as a place of business, a home, a vehicle, acampus, and the like. In one embodiment, the base station 114 b and theWTRUs 102 c, 102 d may implement a radio technology such as IEEE 802.11to establish a wireless local area network (WLAN). In anotherembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.15 to establish a wirelesspersonal area network (WPAN). In yet another embodiment, the basestation 114 b and the WTRUs 102 c, 102 d may utilize a cellular-basedRAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish apicocell or femtocell. As shown in FIG. 1A, the base station 114 b mayhave a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the core network106/107/109.

The RAN 103/104/105 may be in communication with the core network106/107/109, which may be any type of network configured to providevoice, data, applications, and/or voice over internet protocol (VoIP)services to one or more of the WTRUs 102 a, 102 b, 102 c, 102 d. Forexample, the core network 106/107/109 may provide call control, billingservices, mobile location-based services, pre-paid calling, Internetconnectivity, video distribution, etc., and/or perform high-levelsecurity functions, such as user authentication. Although not shown inFIG. 1A, it will be appreciated that the RAN 103/104/105 and/or the corenetwork 106/107/109 may be in direct or indirect communication withother RANs that employ the same RAT as the RAN 103/104/105 or adifferent RAT. For example, in addition to being connected to the RAN103/104/105, which may be utilizing an E-UTRA radio technology, the corenetwork 106/107/109 may also be in communication with another RAN (notshown) employing a GSM, UMTS, CDMA 2000, WiMAX, or WiFi radiotechnology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, 102 d to access the PSTN 108, the Internet 110,and/or the other networks 112. The PSTN 108 may include circuit-switchedtelephone networks that provide plain old telephone service (POTS). TheInternet 110 may include a global system of interconnected computernetworks and devices that use common communication protocols, such asthe transmission control protocol (TCP), user datagram protocol (UDP)and/or the internet protocol (IP) in the TCP/IP internet protocol suite.The networks 112 may include wired and/or wireless communicationsnetworks owned and/or operated by other service providers. For example,the networks 112 may include another core network connected to one ormore RANs, which may employ the same RAT as the RAN 103/104/105 or adifferent RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities (e.g., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks). For example, the WTRU 102 c shown in FIG. 1A may be configuredto communicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram illustrating an example WTRU 102. As shownin FIG. 1B, the WTRU 102 may include a processor 118, a transceiver 120,a transmit/receive element 122, a speaker/microphone 124, a keypad 126,a display/touchpad 128, non-removable memory 130, removable memory 132,a power source 134, a global positioning system (GPS) chipset 136,and/or other peripherals 138, among others. It will be appreciated thatthe WTRU 102 may include any sub-combination of the foregoing elementswhile remaining consistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, in one embodiment,the transmit/receive element 122 may be an antenna configured totransmit and/or receive RF signals. In another embodiment, thetransmit/receive element 122 may be an emitter/detector configured totransmit and/or receive IR, UV, or visible light signals, for example.In yet another embodiment, the transmit/receive element 122 may beconfigured to transmit and/or receive both RF and light signals. It willbe appreciated that the transmit/receive element 122 may be configuredto transmit and/or receive any combination of wireless signals.

Although the transmit/receive element 122 is depicted in FIG. 1B as asingle element, the WTRU 102 may include any number of transmit/receiveelements 122. More specifically, the WTRU 102 may employ MIMOtechnology. Thus, in one embodiment, the WTRU 102 may include two ormore transmit/receive elements 122 (e.g., multiple antennas) fortransmitting and receiving wireless signals over the air interface115/116/117.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 115/116/117from a base station (e.g., base stations 114 a, 114 b) and/or determineits location based on the timing of the signals being received from twoor more nearby base stations. It will be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality, and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs and/or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like. In a case where the peripherals 138 includes oneor more sensors, the sensors may be one or more of a gyroscope, anaccelerometer; an orientation sensor, a proximity sensor, a temperaturesensor, a time sensor; a geolocation sensor; an altimeter, a lightsensor, a touch sensor, a magnetometer, a barometer, a gesture sensor,and/or a humidity sensor.

The WTRU 102 may include a full duplex radio for which transmission andreception of some or all of the signals (e.g., associated withparticular subframes for both the UL (e.g., for transmission) anddownlink (e.g. for reception) may be concurrent and/or simultaneous. Thefull duplex radio may include an interference management unit 139 toreduce and or substantially eliminate self-interference via eitherhardware (e.g., a choke) or signal processing via a processor (e.g., aseparate processor (not shown) or via processor 118).

FIG. 1C is a system diagram illustrating the RAN 103 and the corenetwork 106 according to another embodiment. As noted above, the RAN 103may employ a UTRA radio technology to communicate with the WTRUs 102 a,102 b, 102 c over the air interface 115. The RAN 103 may also be incommunication with the core network 106. As shown in FIG. 1C, the RAN103 may include Node-Bs 140 a, 140 b, 140 c, which may each include oneor more transceivers for communicating with the WTRUs 102 a, 102 b, 102c over the air interface 115. The Node-Bs 140 a, 140 b, 140 c may eachbe associated with a particular cell (not shown) within the RAN 103. TheRAN 103 may also include RNCs 142 a, 142 b. It will be appreciated thatthe RAN 103 may include any number of Node-Bs and RNCs while remainingconsistent with an embodiment.

As shown in FIG. 1C, the Node-Bs 140 a, 140 b may be in communicationwith the RNC 142 a. Additionally, the Node-B 140 c may be incommunication with the RNC 142 b. The Node-Bs 140 a, 140 b, 140 c maycommunicate with the respective RNCs 142 a, 142 b via an Iub interface.The RNCs 142 a, 142 b may be in communication with one another via anIur interface. Each of the RNCs 142 a, 142 b may be configured tocontrol the respective Node-Bs 140 a, 140 b, 140 c to which it isconnected. In addition, each of the RNCs 142 a, 142 b may be configuredto carry out or support other functionality, such as outer loop powercontrol, load control, admission control, packet scheduling, handovercontrol, macrodiversity, security functions, data encryption, and thelike.

The core network 106 shown in FIG. 1C may include a media gateway (MGW)144, a mobile switching center (MSC) 146, a serving GPRS support node(SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each ofthe foregoing elements are depicted as part of the core network 106, itwill be appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The RNC 142 a in the RAN 103 may be connected to the MSC 146 in the corenetwork 106 via an IuCS interface. The MSC 146 may be connected to theMGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices.

The RNC 142 a in the RAN 103 may also be connected to the SGSN 148 inthe core network 106 via an IuPS interface. The SGSN 148 may beconnected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between and the WTRUs102 a, 102 b, 102 c and IP-enabled devices.

As noted above, the core network 106 may also be connected to the othernetworks 112, which may include other wired and/or wireless networksthat are owned and/or operated by other service providers.

FIG. 1D is a system diagram illustrating the RAN 104 and the corenetwork 107 according to an embodiment. As noted above, the RAN 104 mayemploy an E-UTRA radio technology to communicate with the WTRUs 102 a,102 b, 102 c over the air interface 116. The RAN 104 may also be incommunication with the core network 107.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and/or receive wireless signals from, the WTRU 102a.

Each of the eNode-Bs 160 a, 160 b, 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the UL and/or DL, and the like. As shown in FIG. 1D, the eNode-Bs 160a, 160 b, 160 c may communicate with one another over an X2 interface.

The core network 107 shown in FIG. 1D may include a mobility managemententity (MME) 162, a serving gateway (SGW) 164, and a packet data network(PDN) gateway (or PGW) 166. While each of the foregoing elements aredepicted as part of the core network 107, it will be appreciated thatany of these elements may be owned and/or operated by an entity otherthan the core network operator.

The MME 162 may be connected to each of the eNode-Bs 162 a, 162 b, 162 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 162 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 162 may provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM and/or WCDMA.

The serving gateway 164 may be connected to each of the eNode Bs 160 a,160 b, 160 c in the RAN 104 via the S1 interface. The serving gateway164 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 164 may perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when DL data is available for the WTRUs 102 a, 102 b,102 c, managing and storing contexts of the WTRUs 102 a, 102 b, 102 c,and the like.

The serving gateway 164 may be connected to the PDN gateway 166, whichmay provide the WTRUs 102 a, 102 b, 102 c with access to packet-switchednetworks, such as the Internet 110, to facilitate communications betweenthe WTRUs 102 a, 102 b, 102 c and IP-enabled devices.

The core network 107 may facilitate communications with other networks.For example, the core network 107 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 107 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 107 and the PSTN 108. In addition, the corenetwork 107 may provide the WTRUs 102 a, 102 b, 102 c with access to theother networks 112, which may include other wired and/or wirelessnetworks that are owned and/or operated by other service providers.

FIG. 1E is a system diagram illustrating the RAN 105 and the corenetwork 109 according to an embodiment. The RAN 105 may be an accessservice network (ASN) that employs IEEE 802.16 radio technology tocommunicate with the WTRUs 102 a, 102 b, 102 c over the air interface117. As will be further discussed below, the communication links betweenthe different functional entities of the WTRUs 102 a, 102 b, 102 c, theRAN 105, and the core network 109 may be defined as reference points.

As shown in FIG. 1E, the RAN 105 may include base stations 180 a, 180 b,180 c, and an ASN gateway 182, though it will be appreciated that theRAN 105 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 180 a, 180 b,180 c may each be associated with a particular cell (not shown) in theRAN 105 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 117. In oneembodiment, the base stations 180 a, 180 b, 180 c may implement MIMOtechnology. The base station 180 a, for example, may use multipleantennas to transmit wireless signals to, and/or receive wirelesssignals from, the WTRU 102 a. The base stations 180 a, 180 b, 180 c mayalso provide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 182 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 109, and the like.

The air interface 117 between the WTRUs 102 a, 102 b, 102 c and the RAN105 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 109.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 109 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 180 a, 180 b,180 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 180 a, 180 b,180 c and the ASN gateway 182 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 100 c.

As shown in FIG. 1E, the RAN 105 may be connected to the core network109. The communication link between the RAN 105 and the core network 109may be defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 109 may include a mobile IP home agent(MIP-HA) 184, an authentication, authorization, accounting (AAA) server186, and a gateway 188. While each of the foregoing elements aredepicted as part of the core network 109, it will be appreciated thatany of these elements may be owned and/or operated by an entity otherthan the core network operator.

The MIP-HA 184 may be responsible for IP address management, and mayenable the WTRUs 102 a, 102 b, 102 c to roam between different ASNsand/or different core networks. The MIP-HA 184 may provide the WTRUs 102a, 102 b, 102 c with access to packet-switched networks, such as theInternet 110, to facilitate communications between the WTRUs 102 a, 102b, 102 c and IP-enabled devices. The AAA server 186 may be responsiblefor user authentication and for supporting user services. The gateway188 may facilitate interworking with other networks. For example, thegateway 188 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. The gateway 188 may provide the WTRUs102 a, 102 b, 102 c with access to the other networks 112, which mayinclude other wired and/or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1E, it will be appreciated that the RAN 105may be connected to other ASNs, other RANS (e.g., RANs 103 and/or 104)and/or the core network 109 may be connected to other core networks(e.g., core network 106 and/or 107. The communication link between theRAN 105 and the other ASNs may be defined as an R4 reference point,which may include protocols for coordinating the mobility of the WTRUs102 a, 102 b, 102 c between the RAN 105 and the other ASNs. Thecommunication link between the core network 109 and the other corenetworks may be defined as an R5 reference, which may include protocolsfor facilitating interworking between home core networks and visitedcore networks.

Although the WTRU is described in FIGS. 1A-1E as a wireless terminal, itis contemplated that in certain representative embodiments that such aterminal may use (e.g., temporarily or permanently) wired communicationinterfaces with the communication network.

In representative embodiments, the other network 112 may be a WLAN.

A WLAN in Infrastructure Basic Service Set (BSS) mode may have an AccessPoint (AP) for the BSS and one or more stations (STAs) associated withthe AP. The AP may have an access or an interface to a DistributionSystem (DS) or another type of wired/wireless network that carriestraffic in to and/or out of the BSS. Traffic to STAs that originatesfrom outside the BSS may arrive through the AP and may be delivered tothe STAs. Traffic originating from STAs to destinations outside the BSSmay be sent to the AP to be delivered to respective destinations.Traffic between STAs within the BSS may be sent through the AP, forexample, where the source STA may send traffic to the AP, and the AP maydeliver the traffic to the destination STA. The traffic between STAswithin a BSS may be considered and/or referred to as peer-to-peertraffic. The peer-to-peer traffic may be sent between (e.g., directlybetween) the source and destination STAs with a direct link setup (DLS).In certain representative embodiments, the DLS may use an 802.11e DLS oran 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS)mode may not have an AP, and the STAs (e.g., all of the STAs) within orusing the IBSS may communicate directly with each other. The IBSS modeof communication may sometimes be referred to herein as an “ad-hoc” modeof communication.

When using the 802.11ac infrastructure mode of operation or a similarmode of operations, the AP may transmit a beacon on a fixed channel,such as a primary channel. The primary channel may be a fixed width(e.g., 20 MHz wide bandwidth) or a dynamically set width via signaling.The primary channel may be the operating channel of the BSS and may beused by the STAs to establish a connection with the AP. In certainrepresentative embodiments, Carrier Sense Multiple Access with CollisionAvoidance (CSMA/CA) may be implemented, for example in 802.11 systems.For CSMA/CA, the STAs (e.g., every STA), including the AP, may sense theprimary channel. If the primary channel is sensed/detected and/ordetermined to be busy by a particular STA, the particular STA may backoff. One STA (e.g., only one station) may transmit at any given time ina given BSS.

High Throughput (HT) STAs may use a 40 MHz wide channel forcommunication, for example, via a combination of the primary 20 MHzchannel with an adjacent 20 MHz channel to form a 40 MHz wide contiguouschannel.

Very High Throughput (VHT) STAs may support 20 MHz, 40 MHz, 80 MHz,and/or 160 MHz wide channels. The 40 MHz, and/or 80 MHz, channels may beformed by combining contiguous 20 MHz channels. A 160 MHz channel may beformed by combining 8 contiguous 20 MHz channels, or by combining twonon-contiguous 80 MHz channels, which may be referred to as an 80+80configuration. For the 80+80 configuration, the data, after channelencoding, may be passed through a segment parser that may divide thedata into two streams. Inverse Fast Fourier Transform (IFFT) processing,and time domain processing, may be done on each stream separately. Thestreams may be mapped on to the two 80 MHz channels, and the data may betransmitted by a transmitting STA. At the receiver of the receiving STA,the above described operation for the 80+80 configuration may bereversed, and the combined data may be sent to the Medium Access Control(MAC).

Sub 1 GHz modes of operation are supported by 802.11af and 802.11ah. Thechannel operating bandwidths, and carriers, are reduced in 802.11af and802.11ah relative to those used in 802.11n, and 802.11ac. 802.11afsupports 5 MHz, 10 MHz and 20 MHz bandwidths in the TV White Space(TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and16 MHz bandwidths using non-TVWS spectrum. According to a representativeembodiment, 802.11ah may support Meter Type Control/Machine-TypeCommunications, such as Machine Type Communication (MTC) devices in amacro coverage area. MTC devices may have certain capabilities, forexample, limited capabilities including support for (e.g., only supportfor) certain and/or limited bandwidths. The MTC devices may include abattery with a battery life above a threshold (e.g., to maintain a verylong battery life).

WLAN systems, which may support multiple channels, and channelbandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include achannel which may be designated as the primary channel. The primarychannel may have a bandwidth equal to the largest common operatingbandwidth supported by all STAs in the BSS. The bandwidth of the primarychannel may be set and/or limited by a STA, from among all STAs inoperating in a BSS, which supports the smallest bandwidth operatingmode. In the example of 802.11ah, the primary channel may be 1 MHz widefor STAs (e.g., MTC type devices) that support (e.g., only support) a 1MHz mode, even if the AP, and other STAs in the BSS support 2 MHz, 4MHz, 8 MHz, 16 MHz, and/or other channel bandwidth operating modes.Carrier sensing and/or Network Allocation Vector (NAV) settings maydepend on the status of the primary channel. If the primary channel isbusy, for example, due to a STA (which supports only a 1 MHz operatingmode), transmitting to the AP, the entire available frequency bands maybe considered busy even though a majority of the frequency bands remainsidle and may be available.

In the United States, the available frequency bands, which may be usedby 802.11ah, are from 902 MHz to 928 MHz. In Korea, the availablefrequency bands are from 917.5 MHz to 923.5 MHz. In Japan, the availablefrequency bands are from 916.5 MHz to 927.5 MHz. The total bandwidthavailable for 802.11ah is 6 MHz to 26 MHz depending on the country code.

II. D2D

D2D communications using LTE based radio access are designed to operatein either a network-control mode or a UE autonomous mode, hereafterreferred to as Mode 1 and Mode 2, respectively. Mode 1 (networkcontrolled) is only possible if the relay D2D terminal is in radio rangeof a LTE base station. A D2D terminal will fall back to Mode 2 (UEautonomous) operation if it cannot communicate with an LTE base station.In Mode 2, a UE will mostly use channel access parameters pre-stored inthe UE.

For D2D communications in Mode 1, the LTE base station will reserve aselected set of UL subframes for D2D transmissions. The LTE base stationalso may announce a set of UL subframes, including associatedparameters, in which D2D communications for neighbor cells or Mode 2terminals might be received. Not necessarily all LTE system bandwidth(BW) in a subframe that is reserved for D2D may be available for D2Dtransmissions. When operating in Mode 1, radio resources for D2Dcommunications are granted to a D2D terminal by the serving cell. TheD2D grant from the network is preceded by an UL transmission by theterminal using the normal UL channel(s) of the cell indicating to thebase station the amount of D2D data that the terminal wishes totransmit. The D2D grant received by the D2D terminal from the LTE basestation on a DL control channel of the cell will allow the D2D terminalto use certain selected radio resources, i.e., certain resource blocks(RBs) in certain subframes over a certain scheduling period.

In Mode 1, the D2D terminal will transmit a Scheduling Assignment (SA)request message in a first set of one or more D2D subframe(s) and thenit will transmit the D2D data in a second set of D2D subframes in ascheduling period. Scheduling assignments will contain, among otherthings, an identifier field, a Modulation and Coding Scheme (MCS) field,and a resource indicator and Tracking Area (TA) field. D2D data packetscontain, among other things, a Medium Access Control (MAC) header withsource and destination addresses. Multiple logical channels may bemultiplexed and sent as part of a single transport block (TB) in a givenD2D subframe by a UE.

For D2D communications in Mode 2, the D2D terminal selectstime/frequency radio resources autonomously. Channel access parameters,such as the subframes for use with transmissions of SA control messagesand corresponding D2D data, scheduling periods or monitoring subframes,are typically pre-configured and stored on the D2D terminal. Except forthe UL traffic volume indication and the DL D2D grant phase (bothdiscussed above in connection with Mode 1 operation), Mode 2 terminalsfollow essentially the same transmission behavior as Mode 1 terminals,i.e. they will also transmit SA request messages followed by D2D data inscheduling periods.

For D2D communications in both Mode 1 and Mode 2, D2D terminals may alsotransmit auxiliary D2D signals, such as D2D synchronization signals andchannel condition messages (e.g., CQI) to aid receivers in demodulatingthe D2D terminal's transmissions.

D2D communications using LTE based radio access can carry voice channelsor data packets. A special case of D2D communications is D2D discoveryservice. D2D discovery, unlike voice channels, typically requires onlysmall packet transmissions that can often fit in one, two, or a fewsubframes. For example, these packets may contain application dataannouncing availability of devices or software applications toparticipate in D2D data exchanges with terminals in the vicinity.

D2D discovery may or may not use the same channel access protocol as isused for D2D communications for voice or data. For the case of D2Ddiscovery service when in coverage of an LTE base station, D2D discoveryresources can be allocated separately from those used for D2Dcommunications with voice or generic D2D data. Radio resources for D2Ddiscovery messages may be selected autonomously by D2D terminals from aset of resources reserved by the eNB and periodically recurringtime-frequency radio resources in certain UL subframes (Type 1discovery) or they may be explicitly allocated by the LTE serving cellto the D2D terminals (Type 2 discovery). The latter case is similar toD2D communication Mode 1 in that the resources are allocated by thenetwork. On the other hand, it is different in that transmissions ofscheduling assignments are not necessary when transmitting D2D discoverymessages. In some cases, however, even D2D terminals transmitting onlyD2D discovery messages may still be required to transmit auxiliary D2Dsynchronization signals to assist D2D receivers.

There is significant interest in using LTE technology to connect andmanage low cost MTC devices. One important example of such low costdevices are wearables, which also have the benefit of almost alwaysbeing in close proximity to a smartphone that can serve as a relay.

A Study Item (SI) on enhancements to D2D for Wearables and Internet ofThings (IoT) devices has been discussed in 3GPP RAN (See RP-160677,Further Enhancements to LTE Device to Device, UE to Network Relays forIoT and Wearables). In this SI, the aim is to study the application ofD2D, including non-3GPP short-range technologies, to such devices. Inparticular, there are two main aspects to be further enhanced in LTEtechnology to enable D2D-aided wearable and MTC applications, namely,enhancements of UE-to-Network relaying functionality and enhancements toenable reliable unicast PC5 link to at least support low power, lowrate, and low complexity/cost devices. With regard to enhancement ofUE-to-Network relaying functionality, the UE-to-Network relayingarchitecture in ProSe (Proximity Services) does not differentiate thetraffic of the remote UE from that of the relay UE in the accessstratum. This model limits the ability of the network and the operatorto treat the remote UE as a separate device, e.g., for billing orsecurity. In particular, the 3GPP security associations do not extendend-to-end between the network and the remote UE. Thus, the relay UE mayhave unfettered access to the remote UE's communications. This could bea security risk for the remote UE in some cases.

UE-to-Network relaying should be enhanced to support (1) end-to-endsecurity through the relay link, (2) service continuity, (3) E2E QoS(End-to End Quality of Service) where possible, (4) efficient operationwith multiple remote UEs, and (5) efficient path switching between Uuand D2D air-interfaces. Relaying using D2D can also be based on non-3GPPtechnologies such as Bluetooth and Wi-Fi. Some enhancements, such asservice continuity, can make relaying more attractive for suchtechnologies in commercial use cases. This can be especially useful forwearables due to their usage patterns with proximity to the user'ssmartphone, as well as form-factor limitations that may make a direct Uuconnection less practical (e.g., due to limits on battery size).Relaying can enable significant power savings for remote UEs (that aregetting their traffic relayed). This is especially true for deepcoverage scenarios. One cost effective way to introduce relaying is touse unidirectional D2D links between remote devices and relay devices.In such cases, the relay UE is utilized to relay only uplink data fromthe remote UE. The advantage of this approach is that no additional RFcapability for D2D reception is added to the remote UE.

With regard to enhancements to enable reliable unicast PC5 link to atleast support low power, low rate, and low complexity/cost devices, lowcost D2D devices can be enabled by reusing the ideas developed duringNB-IoT (Narrow Band-IoT) and eMTC studies, e.g., the NB-IoT/eMTC uplinkwaveform can be reused for D2D. Such devices will potentially use asingle modem for communicating with the Internet/cloud and forcommunicating with proximal devices. The current PC5 link designinherited from the broadcast-oriented design driven by public safety usecases represents a bottleneck that prevents low power and reliable D2Dcommunication due to lack of any link adaptation and feedbackmechanisms. These shortcomings do not allow achieving target performancemetrics for wearable and MTC use cases in terms of power consumption,spectrum efficiency, and device complexity. Reduced power consumptionand low complexity are the key attributes of wearable and MTC use casesthat are typically characterized by small form factors and long batterylifetime.

FIG. 2 shows the basic architecture for a remote UE 205 and relay UE203, including their connections with an eNB 201. The basic assumptionsin the context of the current SI in 3GPP (see RP-160677, FurtherEnhancements to LTE Device to Device, UE to Network Relays for IoT andWearables) are that: (1) Interface (IF) 1 is a Uu interface between a UEand the eNB; (2) IF2 is a D2D link, which may be PC5, but may also be anon-3GPP link, such as Bluetooth, WiFi, or other non-3GPP links; and (3)IF3 is a Uu interface, which may be assumed to be NB-IoT (i.e., theRemote UE may be in extended coverage with the eNB through NB-IoTrepetitions).

The following options for how data and control information are routedto/from the remote UE over the different interfaces are possible.

First, all control and data to/from remote UE 205 may be sent over IF2.In this case, the remote UE 205, when connected to the relay UE 203,potentially may still listen to broadcast signaling over IF3, but mayalso receive the broadcast signaling from the relay UE 203 as well. Thisscheme results in the maximum power savings for the remote UE.

Alternately, control and data communications may be split. In this case,control information and procedures are performed over IF3, but data(both UL and DL) are transmitted over IF2. In this case, the remote UE205 saves the power associated with transmission and reception of dataover IF2, but not of control information.

In a third option, uplink communications and downlink communications aresplit. In this case, all uplink data (both control and data) is sentover IF2 and all DL data (both control and data) is sent over IF3. Inthis case, the UE saves power by not having to transmit in the uplink.

In a fourth option, the remote UE 205 transmits only the UL user plane(UP) data over IF2. All other traffic (DL UP as well as all controlplane) is transmitted over IF3.

The techniques described in LTE Release 13 for UE to network relays forD2D have several shortcomings which make them less than ideal for IoTand wearable devices. For instance, the wearables and IoT use case isprimarily for commercial use. Currently, there is no interaction betweenthe ProSe Function and the eNB. Since, for commercial uses likewearables and IoT, it is desirable for the eNB to have substantialcontrol over the D2D communications (e.g., determine the resources usedfor D2D communications), the ProSe functionality may need to becompletely replaced or, at least, may have to be significantly modifiedto work in more close association with the eNB or the network. To enablebetter QoS and utilization of resources (to address a potentially largenumber of relays), the network should be given a greater amount ofcontrol as compared to LTE Release 13 relays, including, but not limitedto, being able to trigger the establishment and teardown of relay linksand/or discovery. Furthermore, most wearable devices are likely to bepersonal gadgets. Accordingly, a typical wearable and/or IoT deviceshould be able to connect to only one or a few relay devices inconnection with which it is authorized (e.g., the gadget owner's cellphone and/or tablet). That is, in such cases, the wearable or IoT deviceshould only able to access relay device(s) that it is configured toconnect to instead of attempting to connect to all available relay UEsin proximity. Such procedures need to be clarified and outlined. Evenfurther, the relay schemes in Release 13 are designed for a situation inwhich the remote device does not have connectivity to the networkdirectly. However, the wearables use case generally will present a verydifferent scenario, wherein the wearable device is in the coverage areaof an eNB, but D2D is utilized primarily for power savings purposes.Thus, the connection and coverage assumptions for wearable and IoTrelays is significantly different, leading to different assumptionsrelated to connectivity and access.

For instance, it is not necessary to assume that the remote device doesnot have any direct connectivity with the network. Thus, solutions maytake advantage of D2D relays for some communications but not for others.New control signaling and transport for such control signaling betweenthe remote UE and the network (e.g., NAS) so that the remote UE cancommunicate with the network directly in some regards and through relaysin other regards is desirable. Also, new access mechanisms and discoverymechanisms are desirable to provide greater eNB and network control overD2D communications.

Most of the embodiments discussed below are described for the case ofUEs communicating using D2D under the control of an LTE network.However, such solutions are also applicable to future 5G RAT. Thus,merely as one example, while eNBs are primarily discussed below as thenetwork control point, it should be understood that an eNB is merely anexample, and that the network control point may be a cell, TransmissionPoint (TRP), or equivalent network control point in 5G.

In addition, the D2D links and the associated procedures are mostlydescribed in this disclosure using PC5 (i.e., the traditional LTE D2Dlink). However, again, this is merely exemplary, and other technologiesmay be used, including non-3GPP technologies which are part of the LTEStudy Item (aforementioned RP-160677, Further Enhancements to LTE Deviceto Device, UE to Network Relays for IoT and Wearables) as well as futuredevice to device communication techniques for 5G, including both3GPP-based and non-3GPP based techniques.

II.A. MME Based Relay Selection

The procedures outlined in this section are based on the premise thatthe subscription information of the remote device (e.g., a wearabledevice) is linked to the subscription of the relay device (e.g., acellular telephone or other UE). Particularly, the wearable device andthe relay UE (e.g. smartphone) will commonly be owned by the samesubscriber, and, therefore, the subscription database at the network,e.g., Home Subscriber Service (HSS), may already have information thatlinks the relay node to the wearable device when the wearable device(remote UE) attaches to the network.

FIG. 3A is a signal flow diagram illustrating an exemplary procedure inaccordance with an exemplary embodiment employing MME based relayselection. As shown, during the attach process 301, the wearable UE 313may indicate to the network (MME 317) that it is capable of being aremote UE. Based on such indication, the MME 317 may query the HSS 319(see query 302 in FIG. 3) to request information, e.g., relay UE ID(s),about any UE(s), e.g., UE 311, that are registered with the HSS asassociated with the same user as the wearable UE 313 that may be used asa relay UE for this wearable UE 313. This may be done as part of thesubscription request procedure. As part of the response message 303received from the HSS 319, the MME 317 may receive security informationthat is specific to the remote UE-relay UE connection. It will, ofcourse, be understood by those skilled in the related arts that the NASsignaling between the MME and the UEs may be transported via the eNB315.

Information related to the identity of the relay UE(s) that may beobtained by the MME 317 from the HSS 319 may include, e.g., relay UEID(s) (ID broadcasted by the relay UE for PC5 discovery) and securityinformation, e.g., a special signature(s) which may be used by theremote UE to authenticate the relay UE (described in more detail belowin connection with the PC5 discovery process 306) and vice versa (i.e.,the relay UE may use the same signature to authenticate the remote UE).The MME 317 may forward this information to the remote UE 313 (e.g.,wearable device) in an attach response message 304. Moreover, securitykeys for encrypting the data sent over the PC5 link may also be sent inthe attach response message 304.

Upon completion of the attach process, the wearable UE 313 may initiatethe PC5 discovery process and look for the relay UE(s) 311 based on thereceived relay UE ID(s). This process is represented only generally at305 and 306 in FIG. 3 in order not to obfuscate the drawing. However, itwill be understood that the PC5 discovery process involves varioussignaling between nodes of the network. For instance, the relay UE 311may broadcast its security signature as part of the discovery message(PC5 discovery). The remote UE 313 authenticates the relay UE bycomparing the security signature received over the PC5 discovery channelto the one received in the attach response message 304. The relay UE maybe deemed to be authenticated if the signature matches.

In certain exemplary embodiments, the MME 317 may provide more than onerelay UE to the remote UE in the attach response message 304. This maybe the case if the wearable UE is associated with multiple relay UEsaccording to the subscriber information stored at the HSS 319. Theremote UE 313 may then be adapted to select a specific one of themultiple potential relay UEs in the list to connect to based on certaincriteria, such as any one or more or a combination of (1) measurementsover PC5 as determined during the discovery process (e.g., the remote UEmay simply select the relay UE with the best quality measurements or thefirst relay UE in the list with measurements above a certain threshold),(2) the current loads of the relay UEs (e.g., number of connected remoteUEs) as advertised during discovery (choose the relay UE with the leastnumber of connected remote UEs), (3) a predefined or configurablepreference in the application layer.

The discovery process may be followed by the connection setup orassociation between the remote UE 313 and the relay UE 311. Theconnection setup message 307 sent by the remote UE 313 to the relay UE311 may include the security signature required for the relay UE 311 toauthenticate the remote UE 313. The relay UE 311 may authenticate theremote UE 313 (step 8 in FIG. 3) based on this signature assuming thatit received some security information, e.g., signature context forauthentication and encryption key(s), from the network when it attachedto the network or when the remote UE 313 attached to the network.Alternately, the relay UE 311 may request such security information fromthe network when it receives the connection request 307 from the remoteUE 313. The relay UE 311 authenticates the remote UE 313 based on thereceived security signature (308) and sends a connection response 309 tothe remote UE 313. The connection response message 309 may include therelay UE's security signature.

Data transfer 310 may commence upon completion of the connection setup.Such data transfer may be ciphered by the keys received previously fromthe network both by the remote UE and the relay UE.

Note that the attach request message 304 is merely exemplary in theabove described procedure. Other NAS messages (mobility management,session management or a new NAS message) alternately or additionally maybe used for this purpose in this procedure.

II.B. Remote UE Based Relay Selection

In a remote UE based exemplary embodiment such as illustrated in FIG.3B, the remote UE 313′ may perform PC5 discovery 321, 322 (compare to305, 306 in FIG. 3) before the attach procedure with the network 323,324, 325, 326 (compare to 301, 302, 303, 304 in FIG. 3). By performingPC5 discovery 321, 322, the remote UE 313′ becomes cognizant of theavailable relay UE(s) 311′ in its vicinity. The remote UE 313′, throughthis discovery process, may generate a list of the identities of all theavailable relay UEs (or a subset of the surrounding relay UEs).

The subset may, for instance, be determined based on one or morepredefined criteria such as the Public Land Mobile Network (PLMN) towhich the potential relay UE belongs. For instance, only the relay UEsbelonging to specific PLMNs may be stored by the remote UE. The PLMNinformation may be broadcasted by the relay UE as part of the PC5discovery message or may be part of the broadcasted relay UE ID.Alternately or additionally, only the potential relay UEs that meet asignal level threshold may be selected. Note that, due to the lowtransmission power nature of the remote UEs, the remote may be able tolisten to discovery signals from some of the relay UEs, but not be ableto transmit to them.

Alternately or additionally, the broadcast discovery messages mayinclude an indication of whether the potential relay UE supportsrelaying for wearable devices or IoT devices. Such information may bebroadcast by the relay UE as part of the PC5 discovery message.

Alternately or additionally, the remote UE may consider informationabout the type of service (e.g., health monitoring service) supported bythe relay UE. The relay UE may broadcast the supported services in thePC5 discovery message.

Alternately or additionally, the remote UE may consider the current loadof the relay UE (e.g., in terms of number of remote UEs alreadyconnected to the relay UE).

After the discovery procedure 321, 322, the remainder of the process mayproceed substantially as in FIG. 3A.

For instance, the remote UE 313 may then perform the attach procedurewith the network (compare to 301, 302, 303, 304 in FIG. 3). The attachmessage 323 in this embodiment may differ from that described inconnection with the network based embodiment (FIG. 3A) in that it maycontain the list (Relay UE IDs) of possible relay candidates based onthe aforementioned discovery procedure and criteria for selecting asmaller subset of the possible relay UE(s) as described above. The MME317′ upon receiving this information may check (message 324) the HSS319′ for the subscription profile of the remote UE 313′ and possibly thesubscription information of each of the relay UEs which are part of thelist that is included in the attach message 301 received from the remoteUE. The HSS 319′ should respond (message 325) and the MME 317′ may thenuse the information received from the HSS 319′ in message 325 and theparameters in the attach message 323 to select a relay UE 311′ that theremote UE 313′ should try to connect to. Such relay UE information maybe communicated back to the remote UE in an attach accept message 326.

It may be possible that the MME 317′ selects more than one possiblerelay UE. If such were the case, the MME 317′ may send the associatedpriority of each relay UE in the attach accept message 326. The remoteUE 313′ may start by trying to associate with the relay UE that has thehighest priority (message 327). The relay UE 311′ authenticates theremote UE 313′ based on the received security signature (328) and sendsa connection response 329 to the remote UE 313′. The connection responsemessage 329 may include the relay UE's security signature. Data transfer330 may commence upon completion of the connection setup. Such datatransfer may be ciphered by the keys received previously from thenetwork both by the remote UE and the relay UE.

If the remote UE is unable to connect to that relay UE, it may try toassociate with the next highest ranked relay UE in the priority list andso on. As previously described, the security parameters (authenticationsignature, encryption keys, etc.) may also be sent by the MME forauthentication purpose and ciphering of the user data.

The MME 317′ may consider one or more additional factors apart fromsubscription information to decide the list of relay UEs along withtheir associated priority for the remote UE. For instance, it mayconsider the PLMN IDs of the relay UEs. For example, The MME may onlyallow a remote UE to connect to relay UEs from specific PLMNs takinginto account network sharing agreement with various PLMNs. Alternatelyor additionally, the MME may consider the type (e.g. wearable UE or IoTUE) of the remote UE and/or the number of remote UEs already connectedto the relay UE. The MME may be aware of the type of remote UEs and thenumber of remote UEs connected to a particular relay UE based on themessaging exchange between the relay UE or remote UE and the MME whenthe remote UE connects to the relay UE.

Alternately or additionally, the MME may consider the type of service(e.g. smartwatch, priority service such as health monitoring which isbeing requested by the remote UE). The service information may be partof the attach message or a different NAS message exchange between the UEand the Core Network.

II.C. Core Network Procedures for Remote UE

This section pertains to NAS signaling between the remote UE and thecore network through the relay UE. In other words, it pertains to thecontrol messages (e.g., NAS messages) that are sent by the remote UE tothe relay UE, which the relay UE then forwards to the core network onbehalf of the remote UE (as opposed to the control messages, such asmessages 1 and 4 in FIG. 3, that are transported directly between theremote UE and the network).

The procedures discussed below may be executed when the remote UEdiscovers the relay UE for the first time or once the remote UE receivesan indication or a trigger from the eNB or the network to move traffic,or more specifically control signaling, to the relay node.

II.C.1. NAS Message Transport

The remote UE may send the NAS messages to the relay UE over PC5-S or asidelink channel. It is assumed that there is a sidelink channel forcontrol signaling. Referring to FIG. 4, a new message type (e.g., PDCPSDU Type) 401 or L2 protocol ID (e.g. ProSe Destination L2 ID) may bedefined for NAS messages from the remote UE to the relay UE oversidelink such that the relay UE receiving the control messageunderstands that the control message is a NAS message and is, therefore,to be forwarded to the NAS layer of the relay UE. Alternatively, NASmessages between the remote UE and the relay UE may be transmitted overa separate pool of resources over PC5, or may be identified with adedicated ProSe Per Packet Priority (PPPP) or sidelink logical channel.

FIG. 4 shows an NAS message structure for the relay UE to use forforwarding an NAS message that is received from the remote UE (e.g., viathe aforementioned PC5-S channel or sidelink channel) to the MME (orother network node) according to an exemplary embodiment. A new EPSMobility Management (EMM) message container 405 may be added at the NASlayer. The purpose of such container is to transport remote UE NASmessages to the MME in this container via the NAS signaling connectionbetween the relay UE and the MME. The new EMM 405 container is sent tothe MME in an EMM NAS message (new or existing). A new value for theprotocol discriminator Information Element (IE) 409 is defined so thatthe MME understands that the received message is a NAS message from aremote UE. The MME takes further actions based on the payload of themessage container 405. Note that a similar method may be employed forsession management (SM) messages.

In the downlink, the MME may encapsulate NAS messages intended for theremote UE in an EMM message container 405 in a similar NAS message tothe relay UE. The relay UE, based on the protocol discriminator 409 ofthe incoming NAS message, infers that the message is destined for theremote UE. The NAS layer of the relay UE would further check the EMMmessage container 405 payload to determine the ID, e.g., Globally UniqueTemporary UE ID (GUTI), of the remote UE that the NAS message isintended for. There may be a mapping at the NAS layer between the remoteUE GUTI (identity known at the CN) and sidelink ID (e.g., ProSe ID). Therelay UE then passes the NAS message to the Access Stratum (AS) with theProSe ID, whereby such identity would be used by the AS to transmit themessage to the remote UE over the sidelink. Upon reception of thesidelink message, based on the message type or L2 protocol ID describedearlier, the message is forwarded to the NAS layer in the remote UE.

The NAS messages exchanged between the relay UE and the MME also maycontain a message type in addition to the protocol discriminator, albeitsuch information also may be in the remote UE EMM container with remoteUE NAS payload. Having such information as part of the message may helpthe MME prioritize various requests during periods of high congestion.

II.C.2. Tracking Area Update

The relay UE may perform a Tracking Area Update (TAU) procedure onbehalf of the one or more remote UEs connected to it. It is assumed thatthe relay has up to date knowledge about the remote UE communicatingwith the relay UE. Given this, the remote UE may not have to performtracking area update directly with the MME. Instead the relay UE mayinclude the identities of the remote UEs when performing periodic TAU ornormal TAU procedures. Since the TAU procedure is executed between therelay UE and the MME, the reception of a TAU accept message may not becommunicated to the remote UE(s). However, in certain scenarios, theremote UE may have a need for the information in the TAU response fromthe MME. For example, if the TAU procedure is rejected by the MME, theremote UE may wish to be notified of that fact since the reception of aTAU reject may mean that the remote UE may have to take certain actions,e.g., reattach to the network. PC5-S signaling with a new message typemay be used to communicate such rejection scenarios to the remote UEs.The PC5-S message may also contain the cause code/value indicating thereason for the rejection.

Furthermore, the relay UE may use the NAS transport method describedearlier to send the normal TAU message for an individual remote UE. Thismay happen, for instance, when a particular UE needs to send a normalTAU to reconfigure network parameters, e.g., Power Savings Mode (PSM)timer or change of UE capabilities etc.

If a scenario occurs wherein a remote UE moves out of the coverage ofthe relay UE it has been using and the remote UE is in idle mode, a TAUmay be triggered by the remote UE. This TAU would be sent directly fromthe remote UE to the MME (e.g., using the Uu of the cell) since the“remote” UE would, by definition, no longer be attached to the relay UE.The purpose of such TAU message would be to inform the network that theremote UE is now out of the coverage of the previously connected relayUE. The network may then send all the control signaling to the remote UEdirectly (via the Uu interface). This behavior may continue until theremote UE connects to the same or a different relay node. When theremote UE reconnects to the same or a different relay node, the networkmay then revert back to sending control messages via the relay node.Reception of a TAU message by the network via a relay node may beconsidered to be an indication for the network to transmit MobileTerminated (MT) traffic (both data and signaling) via the relay UE.

III. Conclusion

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer readable medium for execution by a computeror processor. Examples of non-transitory computer-readable storage mediainclude, but are not limited to, a read only memory (ROM), random accessmemory (RAM), a register, cache memory, semiconductor memory devices,magnetic media such as internal hard disks and removable disks,magneto-optical media, and optical media such as CD-ROM disks, anddigital versatile disks (DVDs). A processor in association with softwaremay be used to implement a radio frequency transceiver for use in a WTRU102, UE, terminal, base station, RNC, or any host computer.

Moreover, in the embodiments described above, processing platforms,computing systems, controllers, and other devices containing processorsare noted. These devices may contain at least one Central ProcessingUnit (“CPU”) and memory. In accordance with the practices of personsskilled in the art of computer programming, reference to acts andsymbolic representations of operations or instructions may be performedby the various CPUs and memories. Such acts and operations orinstructions may be referred to as being “executed”, “computerexecuted”, or “CPU executed”.

One of ordinary skill in the art will appreciate that the acts andsymbolically represented operations or instructions include themanipulation of electrical signals by the CPU. An electrical systemrepresents data bits that can cause a resulting transformation orreduction of the electrical signals and the maintenance of data bits atmemory locations in a memory system to thereby reconfigure or otherwisealter the CPU's operation, as well as other processing of signals. Thememory locations where data bits are maintained are physical locationsthat have particular electrical, magnetic, optical, or organicproperties corresponding to or representative of the data bits. Itshould be understood that the exemplary embodiments are not limited tothe above-mentioned platforms or CPUs and that other platforms and CPUsmay support the provided methods.

The data bits may also be maintained on a computer readable mediumincluding magnetic disks, optical disks, and any other volatile (e.g.,Random Access Memory (“RAM”)) or non-volatile (e.g., Read-Only Memory(“ROM”)) mass storage system readable by the CPU. The computer readablemedium may include cooperating or interconnected computer readablemedium, which exist exclusively on the processing system or aredistributed among multiple interconnected processing systems that may belocal or remote to the processing system. It is understood that therepresentative embodiments are not limited to the above-mentionedmemories and that other platforms and memories may support the describedmethods.

In an illustrative embodiment, any of the operations, processes, etc.described herein may be implemented as computer-readable instructionsstored on a computer-readable medium. The computer-readable instructionsmay be executed by a processor of a mobile unit, a network element,and/or any other computing device.

There is little distinction left between hardware and softwareimplementations of aspects of systems. The use of hardware or softwareis generally (but not always, in that in certain contexts the choicebetween hardware and software may become significant) a design choicerepresenting cost vs. efficiency tradeoffs. There may be variousvehicles by which processes and/or systems and/or other technologiesdescribed herein may be effected (e.g., hardware, software, and/orfirmware), and the preferred vehicle may vary with the context in whichthe processes and/or systems and/or other technologies are deployed. Forexample, if an implementer determines that speed and accuracy areparamount, the implementer may opt for a mainly hardware and/or firmwarevehicle. If flexibility is paramount, the implementer may opt for amainly software implementation. Alternatively, the implementer may optfor some combination of hardware, software, and/or firmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples may be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. Suitable processorsinclude, by way of example, a general purpose processor, a specialpurpose processor, a conventional processor, a digital signal processor(DSP), a plurality of microprocessors, one or more microprocessors inassociation with a DSP core, a controller, a microcontroller,Application Specific Integrated Circuits (ASICs), Application SpecificStandard Products (ASSPs); Field Programmable Gate Arrays (FPGAs)circuits, any other type of integrated circuit (IC), and/or a statemachine.

Although features and elements are provided above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. The present disclosure is not to be limitedin terms of the particular embodiments described in this application,which are intended as illustrations of various aspects. Manymodifications and variations may be made without departing from itsspirit and scope, as will be apparent to those skilled in the art. Noelement, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly provided as such. Functionally equivalentmethods and apparatuses within the scope of the disclosure, in additionto those enumerated herein, will be apparent to those skilled in the artfrom the foregoing descriptions. Such modifications and variations areintended to fall within the scope of the appended claims. The presentdisclosure is to be limited only by the terms of the appended claims,along with the full scope of equivalents to which such claims areentitled. It is to be understood that this disclosure is not limited toparticular methods or systems.

It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting. As used herein, when referred to herein, the terms“station” and its abbreviation “STA”, “user equipment” and itsabbreviation “UE” may mean (i) a wireless transmit and/or receive unit(WTRU), such as described infra; (ii) any of a number of embodiments ofa WTRU, such as described infra; (iii) a wireless-capable and/orwired-capable (e.g., tetherable) device configured with, inter alia,some or all structures and functionality of a WTRU, such as describedinfra; (iii) a wireless-capable and/or wired-capable device configuredwith less than all structures and functionality of a WTRU, such asdescribed infra; or (iv) the like. Details of an example WTRU, which maybe representative of any UE recited herein, were provided above withrespect to FIGS. 1A-1E.

In certain representative embodiments, several portions of the subjectmatter described herein may be implemented via Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs),digital signal processors (DSPs), and/or other integrated formats.However, those skilled in the art will recognize that some aspects ofthe embodiments disclosed herein, in whole or in part, may beequivalently implemented in integrated circuits, as one or more computerprograms running on one or more computers (e.g., as one or more programsrunning on one or more computer systems), as one or more programsrunning on one or more processors (e.g., as one or more programs runningon one or more microprocessors), as firmware, or as virtually anycombination thereof, and that designing the circuitry and/or writing thecode for the software and or firmware would be well within the skill ofone of skill in the art in light of this disclosure. In addition, thoseskilled in the art will appreciate that the mechanisms of the subjectmatter described herein may be distributed as a program product in avariety of forms, and that an illustrative embodiment of the subjectmatter described herein applies regardless of the particular type ofsignal bearing medium used to actually carry out the distribution.Examples of a signal bearing medium include, but are not limited to, thefollowing: a recordable type medium such as a floppy disk, a hard diskdrive, a CD, a DVD, a digital tape, a computer memory, etc., and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely examples, and that in fact many other architectures may beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality may beachieved. Hence, any two components herein combined to achieve aparticular functionality may be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediate components. Likewise, any two componentsso associated may also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated may also be viewedas being “operably couplable” to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, where only oneitem is intended, the term “single” or similar language may be used. Asan aid to understanding, the following appended claims and/or thedescriptions herein may contain usage of the introductory phrases “atleast one” and “one or more” to introduce claim recitations. However,the use of such phrases should not be construed to imply that theintroduction of a claim recitation by the indefinite articles “a” or“an” limits any particular claim containing such introduced claimrecitation to embodiments containing only one such recitation, even whenthe same claim includes the introductory phrases “one or more” or “atleast one” and indefinite articles such as “a” or “an” (e.g., “a” and/or“an” should be interpreted to mean “at least one” or “one or more”). Thesame holds true for the use of definite articles used to introduce claimrecitations. In addition, even if a specific number of an introducedclaim recitation is explicitly recited, those skilled in the art willrecognize that such recitation should be interpreted to mean at leastthe recited number (e.g., the bare recitation of “two recitations,”without other modifiers, means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.” Further, the terms“any of” followed by a listing of a plurality of items and/or aplurality of categories of items, as used herein, are intended toinclude “any of,” “any combination of,” “any multiple of,” and/or “anycombination of multiples of” the items and/or the categories of items,individually or in conjunction with other items and/or other categoriesof items. Moreover, as used herein, the term “set” or “group” isintended to include any number of items, including zero. Additionally,as used herein, the term “number” is intended to include any number,including zero.

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein maybe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to”, “at least,” “greater than”, “less than”, and the likeincludes the number recited and refers to ranges which can besubsequently broken down into subranges as discussed above. Finally, aswill be understood by one skilled in the art, a range includes eachindividual member. Thus, for example, a group having 1-3 cells refers togroups having 1, 2, or 3 cells. Similarly, a group having 1-5 cellsrefers to groups having 1, 2, 3, 4, or 5 cells, and so forth.

Moreover, the claims should not be read as limited to the provided orderor elements unless stated to that effect. In addition, use of the terms“means for” in any claim is intended to invoke 35 U.S.C. § 112, ¶6 ormeans-plus-function claim format, and any claim without the terms “meansfor” is not so intended.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, Mobility ManagementEntity (MME) or Evolved Packet Core (EPC), or any host computer. TheWTRU may be used in conjunction with modules, implemented in hardwareand/or software including a Software Defined Radio (SDR), and othercomponents such as a camera, a video camera module, a videophone, aspeakerphone, a vibration device, a speaker, a microphone, a televisiontransceiver, a hands free headset, a keyboard, a Bluetooth® module, afrequency modulated (FM) radio unit, a Near Field Communication (NFC)Module, a liquid crystal display (LCD) display unit, an organiclight-emitting diode (OLED) display unit, a digital music player, amedia player, a video game player module, an Internet browser, and/orany Wireless Local Area Network (WLAN) or Ultra Wide Band (UWB) module.

Although the invention has been described in terms of communicationsystems, it is contemplated that the systems may be implemented insoftware on microprocessors/general purpose computers (not shown). Incertain embodiments, one or more of the functions of the variouscomponents may be implemented in software that controls ageneral-purpose computer.

In addition, although the invention is illustrated and described hereinwith reference to specific embodiments, the invention is not intended tobe limited to the details shown. Rather, various modifications may bemade in the details within the scope and range of equivalents of theclaims and without departing from the invention.

1-51. (canceled)
 52. A method implemented in a first WirelessTransmit/Receive Unit (WTRU) for establishing device to device (D2D)communications between the first WTRU and a second WTRU, the methodcomprising: transmitting to a network node an indication that the firstWTRU is capable of being a remote WTRU for purposes of D2Dcommunications; receiving, from the network node, in response to theindication, a response identifying at least one second WTRU associatedwith the first WTRU and authorized to act as a relay node for the firstWTRU in D2D communications.
 53. The method of claim 52 wherein theindication is included in an attachment request.
 54. The method of claim52 wherein the network node is a Mobility Management entity (MME). 55.The method of claim 52 wherein the response includes securityinformation for communications between the first WTRU and the at leastone second WTRU.
 56. The method of claim 55 wherein the securityinformation comprises a signature associated with the at least onesecond WTRU.
 57. The method of claim 55 wherein the security informationcomprises an encryption key for use by the first WTRU in communicationswith the second WTRU.
 58. The method of claim 52 further comprising:performing a discovery process to discover the at least one second WTRU.59. The method of claim 52 wherein the at least one second WTRUcomprises a plurality of WTRUs, the method further comprising: selectingone of the plurality of second WTRUs to serve as a relay node for D2Dcommunications.
 60. The method of claim 59 wherein the selectingcomprises selecting based on at least one measurement over a PC5connection during the discovery process.
 61. The method of claim 60wherein the selection is further a function of a current load of each ofthe plurality of second WTRUs.
 62. The method of claim 61 wherein thecurrent load is a function of a number of WTRUs currently using therespective second WTRU as a relay node for D2D communications.
 63. Themethod of claim 60 wherein the selection is further a function of a apreference in the application layer.
 64. A first WirelessTransmit/Receive Unit (WTRU) comprising: a transmitter; a receiver; anda processor configured to control the transmitter to transmit to anetwork node an indication that the first WTRU is capable of being aremote WTRU for purposes of D2D communications; the processor furtherconfigured to control; the receiver to receive, from the network node, aresponse to the indication identifying at least one second WTRUassociated with the first WTRU that is authorized to act as a relay nodefor the first WTRU in connection with D2D communications.
 65. The methodof claim 64 wherein the indication is included in an attachment request.66. The method of claim 64 wherein the response includes securityinformation for communications between the first WTRU and the at leastone second WTRU.
 67. A method implemented in a first WirelessTransmit/Receive Unit (WTRU) for establishing device to device (D2D)communications between the first WTRU and a second WTRU, the methodcomprising: performing a D2D discovery process to discover other WTRUsin the vicinity of the first WTRU that are potential relay nodes for thefirst WTRU for D2D communications; transmitting to a network node anindication that the first WTRU is capable of being a remote WTRU forpurposes of D2D communications and a list of the WTRUs discovered in thevicinity of the first WTRU; receiving, in response to the indication, aresponse including an identity of at least one second WTRU that isassociated with the first WTRU and authorized to act as a relay node forD2D communications with the first WTRU, the at least one second WTRUbeing one of the WTRUs in the list transmitted by the first WTRU. 68.The method of claim 67 wherein the indication and the list are includedin an attachment request.
 69. The method of claim 67 wherein the networknode is a Mobility Management Entity (MME).
 70. The method of claim 68wherein the response includes security information for communicationbetween the first WTRU and the at least one second WTRU.
 71. The methodof claim 67 wherein the at least one second WTRU comprises a pluralityof WTRUs and wherein the response from the network node includes aranking of the plurality of second WTRUs.